Mahaleb rootstock named ‘UCMH 55’

ABSTRACT

A new and distinct cultivar of  Prunus mahaleb  is provided. The new cultivar is particularly well suited for serving as an understock during cherry production. A number of advantages are provided when compared to the standard Mahaleb rootstock. The cultivar is readily amenable to vegetative propagation (e.g., by the use of softwood cuttings), and exhibits improved resistance to Phytophthora spp. When used with a ‘Bing’ cherry scion, increased yields have been observed. The new cultivar when grown without use as an understock forms a tree that is intermediate in size and forms more fine wood when compared to the ‘UCMH 56’ and ‘UCMH 59’ cultivars that were products of the same research program.

Botanical/commercial classification: Prunus mahaleb/Mahaleb Rootstock.

Varietal denomination: cv. ‘UCMH 55’.

SUMMARY OF THE INVENTION

Mahaleb rootstocks (i.e., Prunus mahaleb rootstocks) are widely usedduring both sweet and sour cherry production throughout the world. Ithas been the common practice to form such rootstock plants from seedfollowing the random outcrossing of parent plants. Accordingly, cherryproduction encountered when using such plants as an understock hastended to be somewhat variable due to differences in the genotype of theunderstock. Such variation often has led to reduced field performance onsome cherry trees on a random and unpredictable basis. Mahalebrootstocks in the past have generally been found to be incapable ofvegetative propagation on a reliable basis, such as through the use ofsoftwood and hardwood cuttings. Also, such rootstocks in the past havebeen susceptible to root and crown fungal diseases generally known asPhytophthora spp.

SUMMARY OF THE NEW CULTIVAR

It was an object of my research to provide Prunus mahaleb rootstocksthat possess characteristics that overcome shortcomings of the Mahalebrootstock presently being used during cherry production. Morespecifically, it was my goal to provide cherry rootstocks that could bevegetatively propagated in an expeditious and reliable manner so thatcherry growers can eliminate crop variation that can be traced to lackof uniformity in the rootstock. Also, it was a goal of my research toprovide new Mahaleb rootstocks that inherently display needed resistanceto disease and thereby make possible a satisfactory cherry crop on amore consistent basis combined with a reduction in the need to replantbecause of tree loss that is traceable to disease.

The original tree of the new Prunus mahaleb cultivar of the presentinvention was discovered through detailed evaluation and selection whilegrowing in a cultivated area at the Experimental Orchards at theUniversity of California located at Davis, Calif., U.S.A. The exactparentage of the new cultivar is unknown. The seeds used to form theplanting where the discovery took place came from a random collection ofwild Prunus mahaleb germplasm that had been collected from around theworld. The large number of seedlings present in the planting werecarefully studied and evaluated and a single plant possessing thecombination of characteristics of the new cultivar of the presentinvention was selected and was preserved. Accordingly, the plant of thenew cultivar was produced by the hand of man and was not found whilegrowing in the wild. Had this plant not been discovered and preserved,it would have been lost to mankind.

Other Prunus mahaleb cultivars resulting from the same research are‘UCMH 56’ (U.S. Plant patent application Ser. No. 10/028,772, filedconcurrently herewith), and ‘UCMH 59’ (U.S. Plant patent applicationSer. No. 10/029,284, filed concurrently herewith).

It was found that the new Prunus mahaleb cultivar of the presentinvention exhibits the following combination of characteristics:

(a) readily is amenable to vegetative propagation,

(b) performs well as an understock for cherry production,

(c) forms a tree that is intermediate in size and forms more fine woodwhen compared to the ‘UCMH 56’ and ‘UCMH 59’ cultivars, and

(d) displays improved resistance to Phytophthora spp.

In view of the above combination of characteristics, the new cultivar ofthe present invention well meets the needs of cherry producers for useas an improved rootstock. Cherry scion characteristics are no longerinfluenced by variation in the Mahaleb rootstock resulting from therandom outcrossing of parental plants. Also, the disease resistance madepossible by the new cultivar is a major advantage for cherry producers.

The new cultivar of the present invention has been repeatedly reproducedthrough the use of softwood and hardwood cuttings at Davis, Calif.,U.S.A. Such propagation has confirmed that the characteristics of thenew cultivar are stable and are firmly fixed and are transmitted tosubsequent generations on a reliable basis.

The new cultivar of the present invention initially was designated ‘UCMahaleb 155-1’, and subsequently has been named ‘UCMH 55’.

BRIEF DESCRIPTION OF THE PHOTOGRAPHS

The accompanying photographs show specimens of the plant and plantparts, and also provide DNA information concerning the new cultivar ofthe present invention. Color is shown as nearly true as is possible tomake the same in color illustrations of this character. The trees of thenew cultivar were grown at the Experimental Orchards of the Universityof California located at Davis, Calif., U.S.A.

FIG. 1 shows a tree of approximately 5 to 7 years of age duringDecember. The tree is a mother plant that was being used to makepropagules for additional testing and evaluation. Most of the leaves haddropped by the end of the preceding October.

FIG. 2 shows a specimen of a current season's shoot with leavescollected during mid-October. Such shoot was suitable for use to make ahardwood or semi-hardwood cutting.

FIG. 3 shows a specimen of typical branch tip with buds of the newcultivar during the winter. Dimensions in centimeters and inches areincluded.

FIG. 4 shows specimens of typical branches with dried fruit of the newcultivar during the winter. Dimensions in centimeters and inches areincluded.

FIG. 5 shows the DNA fingerprint of the new cultivar of the presentinvention as well as that of the ‘UCMH 56’ and ‘UCMH 59’ cultivars forcomparative purposes. Three microsatellite markers were used during theDNA determinations (i.e., PMS30, PMS40 and PMS15). Data with respect tothe plants of the new cultivar of the present invention is designated“155-1”. Data with respect to the plants of the ‘UCMH 56’ cultivar isdesignated “156-5”, and data with respect to the ‘UCMH 59’ cultivar isdesignated “159-5”.

FIG. 6 shows typical inflorescences of the new cultivar.

The primer sequences (SEQ ID Nos.: 1-6) used in this determination areas follows:

PMS 30 Forward CTG TCG AAA TGC CTA TGC Reverse ATG AAT GCT GTG TAC ATGAGGC, PMS 40 Forward TCA CTT TCG TCC ATT TTC CC Reverse TCA TTT TGG TCTTTG AGC TCG, PMS 15 Forward TCC GCT TCT CTG TGA GTG TG and Reverse CGATAG TTT CCT TCC CAG ACC.

When preparing the DNA fingerprints, a total of six leaf samples wererandomly collected from two different but replicate trees. Accordingly,each genotype was sampled and replicated twice. The two samples aredistinguished during the presentation of data by the final digit shownin FIG. 5 (i.e., by “−1” or by “−2”). DNA was extracted using DneasyPlant Kit from Qiagene, Inc. (Valencia, Calif., U.S.A.) following themanufacturer's protocol. The extracted DNA was purified by adding{fraction (1/10)} volume 3M sodium acetate and 2 volumes 100 percentethanol and subsequent storage at −20° C. for an hour. The samples werecentrifuged at 13,000 rpm for 15 minutes and the pellets were washed twotimes with 70 percent ethanol. The pellets were air dried and resolvedin 50 μl TE buffer. Quantification of DNA was performed with ethidiumbromide agarose gel plates. PCR was carried out under the followingconditions: 100-150 ng of template DNA, 250 nM of each primer, 200 μM ofdNTPs, 0.5 U of Taq Polymerase, and 1.5 mM of MgCl₂. The reaction wasrun for 45 cycles (denaturing at 94° C. for 1 minute, annealing at 60°C. for 1 minute, with a two minute extension at 72° C.), followed by asingle extension at 72° C. for 60 minutes. The amplification productswere detected on 5.5 percent polyacrylamide gels using a Li-Cor IR² 4200DNA sequencer (Li-Cor, Nebraska, U.S.A.). The three microsatellitemarkers clearly distinguished the three cultivars. Both repeats of eachrootstock showed identical fingerprints. The marker PMS30 produced twobands for rootstock ‘UCHM 55’ at 132bp (base pair) and 159bp, two bandsfor ‘UCMH 56’ at 132bp and 168bp, and one band for ‘UCMH 59’ at 142bp.Marker PMS40 produced two bands for ‘UCMH 55’ at 92bp and 111bp, and oneband for ‘UCMH 56’ at 92bp, and two bands for ‘UCMH 59’ at 92bp and129bp. Marker PMS15 produced two bands for ‘UCMH 55’ at 118bp and 128bp,two bands for ‘UCMH 56’ and 112bp and 123bp, and two bands for ‘UCMH 59’at 105bp and 115bp.

FIG. 6 shows a typical inflorescence.

DETAILED DESCRIPTION

The following is a detailed description of the new cultivar. The treewas grown at the Experimental Orchards of the University of Californiaat Davis, Calif., U.S.A. Color designations are presented with referenceto the “Dictionary of Color” by Maerz and Paul, First Edition (1930).

Tree:

Size.—Intermediate to the ‘UCMH 56’ and ‘UCMH 59’ cultivars. An eightyear-old tree of the ‘UCMH 55’ cultivar that has undergone some pruningcommonly will display a height of approximately 4 meters and a width ofapproximately 3 meters. Trunk girth at 30 cm above the soil linecommonly will possess a cross-sectional area of approximately 400 cm².

Growth.—Spreading, the upper canopy is very upright, and two-year-oldwood in the lower canopy is pendulous. All wood is very fine. Forms morefine wood than the ‘UCMH 56’ and ‘UCMH 59’ cultivars.

Bark.—Possesses a rough raised surface and an Iron grey (24 A 2)coloration.

Branches:

Shoot growth form.—Straight with spirally-arranged leaves, (single ateach node), laterals are highly branched and secondaries are mostlyunbranched, and laterals arise at approximately 75 to 90 degrees fromthe point of origin on the main scaffold.

Size.—Both current and previous season wood is fine and commonlydisplays a diameter of less than 1 cm.

Spurs.—Commonly 9 to 16 spurs are present per 85 cm of previous seasonshoot that measure approximately 5 to 7 cm in length. The coloration isChickadee gray (47 A 1) underlaid with Malaga (7 L 1).

Internode length.—Internodes of mixed shoots having a length ofapproximately 40 to 100 cm commonly vary in length from approximately1.3 to 3.6 cm.

Shoot bark.—Smooth in texture, and the coloration is light brown with asilvery cast varying from Arabian night brown (14 A 11) to 14 G 8.

Main scaffold bark.—Platinum (45 A 3) in coloration with an underlay ofRubient (55 L 8).

Lenticels.—Prominent, densely distributed, and under magnification areraised. On the main scaffold and lower large limbs the coloration isParchment (12 B 3). On the shoot bark the length commonly ranges fromapproximately 2.5 to 5 mm and the coloration is Iron grey (24 A 2). Onthe subsidiary branches the length commonly ranges from approximately 2to 5 mm, the frequency is approximately 8 per square inch, and thecoloration is Parchment (12 B 3).

Axillary buds.—Borne on spurs of varying length on previous seasongrowth axillary, imbricate, sessile, and single. The bud tips arepointed and the bud pose is adpressed on dormant new wood. The budsupport is small. Vegetative buds proximal to the reproductive portionof the shoot commonly are borne spirally.

Leaves:

Bearing.—Simple, spirally-arranged and petiolate.

Pose.—Curved outward and downward and often curl under slightly at theapex.

Length.—Approximately 5 to 6 cm in length excluding the petiole andapproximately 3 to 4.5 cm in width on the upper canopy and on the lowercanopy.

Width.—Approximately 3 to 4.5 cm on the upper canopy and on the lowercanopy.

Form.—Oval-elliptic to oval with an acuminate tip and a truncate base onthe upper canopy and on the lower canopy.

Margins.—Crenate and glandular between rounded teeth.

Surfaces.—Glabrous on the dorsal and ventral surfaces with short stiffhairs along the midrib of the ventral surface that are visible withmagnification.

Petiole.—Commonly with glands that are dark Russet brown (14 I 12) atthe leaf-petiole juncture, approximately 1.5 to 2 cm in length, andRusset green (20 K 1) in coloration on the upper canopy and on the lowercanopy. Such glands commonly are less than 1 mm in length and less than0.5 mm in width.

Venation.—Pinnate, with the midrib and other venation being Russet green(20 K 1) in coloration.

Color.—21 L 6 (Parrot Green) to 21 L 9 on the upper surface and Piquantgreen (20 K 6). on the under surface.

Leaf drop.—On Dec. 11, 2000 there was approximately 95 percent leaffall.

Bloom time.—Full bloom on Mar. 29, 2002.

Floral buds.—Approximately 2 mm in length and approximately 1 mm inwidth, and Burmese ruby (7 H 6) in coloration.

Flowers:

Type.—Single or inflorescent in panicles.

Form.—The paniculate inflorescence commonly has approximately 8 to 14flowers with a peduncle including rachis of approximately 2.5 to 4 cm inlength and a pedicel of approximately 1.5 to 2 cm in length. Anthesisproceeds acropetally within the inflorescence. The paniculateinflorescence commonly bears one or two bracts at the base of or on thepeduncle and a single bract at the base of the pedicel.

Bearing.—Inflorescences of approximately 8 to 14 flowers are bornespirally as well as single flowers on previous season laterals. Fruitbearing wood may be a 1 or 2 degree lateral, a mixed shoot in that theproximal portion (½ to ¾ of the shoot) is vegetative with axillaryshoots that break after flowering, and with the distal portion of oneyear-old wood that bears single flowers or inflorescences directly onthe fruit wood in the absence of spurs. The terminal bud is commonly amixed vegetative bud (leaves and shoot).

Pollination required.—Any Mahaleb rootstock that is producing flowerswhich overlap with the bloom period.

Color.—White.

Petal number.—Five.

Petal size.—Approximately 6 mm in length and approximately 4 mm in widthat the widest point.

Sepals.—Five.

Carpel.—Single with two ovules one of which commonly aborts.

Pistil.—Approximately 3.5 to 4 mm in length with the stigma and stylebeing Marguerite Yellow (10 C 1) in coloration.

Stamen.—Commonly approximately 11 to 16 per flower, and approximately 6to 7 mm in length.

Anthers.—Cossak green (23 L 11) in coloration when indehiscent.

Filaments.—Marguerite Yellow (10 C 1) in coloration.

Pollen.—Cossak green (23 L 11) in coloration.

Scent.—Mildly fragrant and similar to that of almond flowers.

Fruit:

Chilling requirement.—Approximately 750 to 1,000 hours less than orequal to 45° F.

Bearing.—Drupe.

Maturity date.—Late June to early July.

Skin color.—Dark purple-mahongany (56 A 12) to near back (48 A 12).

Flesh color.—Dark purple-mahogany (56 A 12) to near black (48 A 12).

Flesh firmness.—Soft when fully ripe and juicy.

Cracking susceptibility.—None observed during observations to date.

Eating quality.—Astringent and bitter taste renders unsuitable foreating.

Shape.—Oval and pointed at the pistillate end.

Size.—Approximately 1.5 to 2 cm in diameter.

Juice color.—Dark purple-mahogany (56 A 12) to near black (48 A 12).

Fruit stalk.—Short, approximately 1 to 1.8 cm. One or two very smallbracts commonly persist at the base of the inflorescence. Such bractsare Paradise green (22 L 11) in coloration.

Fruit drop.—Susceptibility is high (approximately 50 to 100 percent).

Stone shape.—Substantially spherical.

Stone size.—Intermediate and approximately 7 to 8 mm in diameter.

Seed color.—Oyster white (10 B 1).

Disease resistance: The new cultivar has shown 100 percent survival ratein field trials at sites that are heavily infested with Phytophthoraspp. and stem pitting virus. At the same sites, approximately 50 percentof the standard Mahaleb plants died.

Vegetative propagation: The new cultivar asexually reproduces wellthrough the rooting of softwood and hardwood cuttings. The use ofsoftwood cuttings is preferred.

Use as a scion rootstock: Field testing has been conducted using a scionof ‘Bing’ cherry following budding. Precocious flowering and croppingare facilitated when using the new cultivar as a rootstock. Forinstance, flower and fruit production can begin easily in the 4th or 5thgrowing season with the flowers opening earlier in the season. The fruitsize has been found to be comparable to that formed with standardMahaleb rootstock. To date the new cultivar produced low numbers of rootand crown suckers.

6 1 18 DNA Artificial Sequence PMS 30 forward primer 1 ctgtcgaaatgcctatgc 18 2 22 DNA Artificial Sequence PMS 30 reverse primer 2atgaatgctg tgtacatgag gc 22 3 20 DNA Artificial Sequence PMS 40 forwardprimer 3 tcactttcgt ccattttccc 20 4 21 DNA Artificial Sequence PMS 40reverse primer 4 tcattttggt ctttgagctc g 21 5 20 DNA Artificial SequencePMS 15 forward primer 5 tccgcttctc tgtgagtgtg 20 6 21 DNA ArtificialSequence PMS 15 reverse primer 6 cgatagtttc cttcccagac c 21

I claim:
 1. A new and distinct cultivar of Prunus mahaleb plant thatexhibits the following combination of characteristics: (a) readily isamenable to vegetative propagation, (b) performs well as an understockfor cherry production, (c) forms a tree that is intermediate in size andforms more fine wood when compared to the ‘UCMH 56’ and ‘UCMH 59’cultivars, and (d) displays improved resistance to Phytophthora spp.;substantially as illustrated and described.